Sports surface

ABSTRACT

A sports surface is disclosed with upstanding synthetic yarn tufts which simulate blades of grass. The blades are widely spaced and supported by an under layer of high denier, knit-deknit yarn tufts, without the need of particulate in-fill.

BACKGROUND FIELD OF THE INVENTION

[0001] The present invention relates to synthetic sports surfaces and, in particular, synthetic grass turf with upstanding grass-blade-like tufts of polymer yarn.

BACKGROUND AND OBJECTS OF THE INVENTION

[0002] Synthetic turf was originally developed in response to a need for a sports playing surface which could overcome some of the limitations of natural grass turf. The advent of the covered, multipurpose stadium was the impetus of the original development.

[0003] The expectation was that the relatively high cost of building the facility could be recovered by using the facility not only for football and baseball but also for many other events (e.g., circuses, rodeos, professional wrestling, basketball, soccer, track meets, trade shows and even political conventions). It was quickly recognized that natural turf could not be practically grown indoors, particularly if it was to be in use a high percentage of the time. Natural turf could not be grown with so little sunlight and required relatively long periods of time between events to allow the natural turf to recover from the abuse caused by the events. The solution to this problem was a new type of carpeting designed for multipurpose use with a particular emphasis on the two major sports (football and baseball) that were to be the major users of the facility (but not the only users).

[0004] Once it was understood that a carpet could be used for football and baseball at the major league level and that the carpet could be used far more frequently then natural turf, a broader market rapidly developed. Numerous high school and colleges installed synthetic turf football fields, particularly in the arid southwest where the hot, dry climate made it very difficult to grow grass. Prior to that time the norm for the natural grass fields had been to start a football or baseball season with the field in the best condition possible, depending on the weather. The field would gradually deteriorate as it was used. Many football fields had little or no grass left in the center of the field long before the last game of the season was played.

[0005] Traditional synthetic turf products employed a nylon monofilament fiber or a polypropylene fibrillated film fiber in a relatively dense, low pile height carpet (pile height less than about one inch). This form of sport surface, although very durable and long wearing, has fallen out of favor for use in soccer and football.

[0006] The traditional low pile height carpet is now being replaced by sports surfaces made of polyethylene (PE) fibrillated film fiber with a much greater pile height. These sport surfaces are being tufted in a more open, higher pile height construction with only ⅓ to ½ the face weight of fiber. The PE material has an inherently more slippery surface, than either the polypropylene or Nylon fiber that it is replacing, and a lower flexural modulus. The taller PE fiber does not stand straight up, but leans or lies to one side. The playing action then takes place on the sides of the fiber as opposed to the tips of the fiber. Playing on the sides of the more slippery PE fiber reduces the traction level for football and reduces the frequency of skin burns in soccer.

[0007] The traditional carpet was designed using generally accepted principles for long wearing durable carpets. This meant that the pile height was kept below one inch and that the face yarn content was generally maximized. This construction reduces the movement between fibers and also the opportunity for dirt or sand to get in between the fibers. This prolongs the useful life of the carpet by reducing the movement of the face fiber. It is possible to extend the useful life of the carpet by minimizing fiber-to-fiber abrasion, and also fiber abrasion by even more abrasive dirt and sand.

[0008] Typically, the new carpet construction, involves higher pile height (greater than 1 inch, and preferably 2 to 3 inch pile height). The face weight of fiber is reduced by using a wider gauge tufting machine (⅜ inch to as wide as ¾ inch tuft separation) and the stitch rates are designed to further produce an even more open construction (3 to 4 stitches/inch). The typical face weight of fiber is in the 30 to 40 oz per square yard range. The use of a higher pile height and wide gauge tufting machine produces a carpet with much less fiber density per square yard than has been used in the past.

[0009] The new high pile height and open construction approach has two major purposes. First it produces a face fiber that is similar to natural grass in pile or turf height, and it is close in appearance to natural grass in the way it leans over and also in density of the tufts. Second, the open construction and the high pile height make possible an entirely new approach to the padding. The carpet is installed on the field and then in-filled to a depth of ¼ to 1 inch with rubber, sand or a combination of these materials. The in-fill material is then brushed with a coarse brush or a rotary powered brush (similar to a street cleaning brush) until the in fill material settles down, and into the tufted carpet (largely out of view). The in-fill is soft which can give the finished field a feel under foot similar to good natural turf sod.

[0010] U.S. Pat. No. 5,958,527 to Pr{overscore (e)}vost (Fieldturf) discloses a synthetic grass turf assembly including upstanding synthetic ribbons representing grass blades and an in-fill of particulate material including sand granules and rubber granules. The upper portion of the ribbons may extend upwardly from 0.25 to 1 inch above the top surface of the in-fill.

[0011] A product marketed as AstroPlay™ Synthetic Turf Systems by Southwest Recreational Industries, Inc., employs a polyethylene fiber with a pile height of 2.3 inches and a fiber denier of 7600 or 10,000. A 100% rubber filing is said to prevent grinding and compaction associated with sand in-fills. A secondary layer of highly texturized nylon 6.6 fibers is provided at the base of the taller polyethylene turf fiber matrix. The stated purpose of this secondary layer is to enmesh the initial layer of rubber filling and thus stabilize the fill.

[0012] While the above-described surfaces with in-fill can provide an installed carpet that looks and feels more like natural turf than the dense tight carpet it is replacing, it is not likely to wear as well. There is the potential for accelerated wear due to increased fiber-to-fiber abrasion and fiber to sand/rubber abrasion. Sand fills may be subject to compaction and contamination. Rubber fills may migrate and degrade.

[0013] A large source of complaints regarding in-filled carpets are related to defective installation. One source of difficulties may arise from the need to mix filler (blending rubber and sand) on site. The in-fill must then be brushed or raked into the carpet. (This is often done with a powered rotary brush similar to that used for street cleaning). The brushing can subject the new sports surface to some significant abuse during the installation process. The specifications for the in-fill typically spell out a uniform depth or weight per square yard. However, it is difficult to achieve uniformity under field conditions and a wide variation in the depth and/or weight of the in-fill material may occur. Later as the carpet is used and subjected to heavy rain and snow the in-fill distribution may change, e.g., an all-sand in-fill may compact and becomes increasing harder with age; and a blend of sand and rubber in-fill may tend to stratify by density (the sand sinks and the rubber comes to the top). Where most or all the rubber in-fill is located on top, the rubber has a tendency to be washed out of the carpet where drainage occurs.

[0014] Accordingly, it is an object of the present invention to provide a sport surface which reduces the limitations and difficulties associated with conventional sports surfaces.

[0015] It is another object of the present invention to provide a sports surface which is durable and stable.

[0016] It is another object of the present invention to provide a sports surface with cushioning firmness and frictional properties appropriate to the playing of the sport(s) for which the surface is installed.

[0017] It is another object of the present invention to provide a grass-like sports surface which is easily and inexpensively fabricated and installed.

[0018] It is another object of the present invention to provide an improved sports surface which can be made on conventional tufting machines.

[0019] These and other objects and features of the invention will be apparent from the following description and drawings.

SUMMARY OF INVENTION

[0020] The present invention includes a synthetic sports surface made of a flexible backing tufted with a novel combination of yarns of different final lengths and textures. A first yarn is tufted at spaced intervals in said backing to provide first yarn segments extending upwardly from the backing suggestive of blades of grass. At least a second type of yarn is tufted in the intervals between said first yarn, to provide second yarn segments. The second yarn segments may be of a conventional texturized yarn having a length under tension approximately equal to that of the first yarn segments. In the finished surface the second yarn segments return to a sinusoidal or kinked form and constitute an under layer having a lower vertical height than the first yarn segments.

[0021] Advantageously, the second yarn segments are sufficiently numerous and of sufficient dimension and texture so as to maintain the bases of the first yarn segments in an approximately vertical orientation without requiring the provision of a particulate fill.

[0022] In preferred embodiments the second yarn is a conventional knit-deknit yarn having a kinked form. In more preferred embodiments, the second yarn has a denier of at least 7000.

[0023] The synthetic sports surface of the present invention may further include a third yarn tufted in the intervals between the first and second yarn tufts to provide third yarn segments, which together with the second yarn segments form an intertwined mat which maintains the first yarn segments in an approximately vertical orientation. Third and subsequent yarn segments forming the intertwined mat may all be knit-deknit textured yarn.

[0024] The first yarn may be a twisted or flat fibrillated, polyethylene tape. The first yarn segments extend upwardly from the backing from 1 to 3 inches. In preferred embodiments the first yarn is made from a thermoplastic having a coefficient of friction lower than unmodified nylon. The first yarn may be made from a nylon modified with an additive for lowering the coefficient of friction selected from the group comprising silicone and Teflon. Various combinations of yarn types are possible such as first, second and third yarns of different denier, color, composition and texture.

[0025] In accordance with the foregoing teachings, a game playing surface may be provided having first upstanding tufts of polymeric yarn at least one inch in length and having second tufts of generally sinusoidally curved yarn located around the upstanding tufts, the first tufts extending upwardly beyond the second tufts. At least about half of the yarn face weight may be contained in the second tufts.

[0026] The present invention also includes a method of making a sports surface. In accordance with that method, a carpet tufting machine is used to produce lines of tufts in a backing with a separation distance S. A first yarn is fed to the tufting machine for producing first tufts at line separations no less than twice S to form tufts of vertical length L. A second knit-deknit yarn is fed to the tufting machine for producing second tufts between the first tufts, the second tufts having a length under tension approximately equal to the height L. The tufted backing is then heat treated to cause the yarn of the second tufts to tend to return to its knit shape, thereby forming a supporting base for maintaining the first tufts in an approximately vertical orientation.

[0027] Using more fiber in place of the more abrasive in-fill and increasing the fiber density will result in a longer wearing carpet. Controlling the fiber density and creating more than one level of yarn within the carpet can adjust the firmness under foot. Controlling tufting machine gauge, stitch rate and finished pile height does this. It is also possible to use different combinations of fiber (different deniers, different colors and polymer type) to combine the benefits of different fibers within one carpet. The different fibers can include fibrillated film fiber made from polyethylene, polypropylene or Nylon resin. The denier of the tufted yarns can be from 1,850 to 15,000 denier.

[0028] The sports surface construction of a preferred embodiment of the present invention need not rely on the field installation to provide in-fill and, thus, would not require that the carpet be subjected to any rotary brushing. Once installed there is no need for particulate in-fill. Cushioning is achieved using a dense combination of multiple pile heights and yarn textures that will stay in place. The total weight of fiber is inherently much greater and the life expectancy of the sports surface is improved by reducing fiber-to-fiber abrasion and fiber to sand/rubber abrasion. While such a sports surface may be somewhat more expensive initially due to the greater weight of yarn used, this cost may be offset by the cost savings associated with simplified installation and longer life of the sports surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a side elevation of a prior art sports surface based on FIG. 2 of U.S. Pat. No. 5,958,527;

[0030]FIG. 2 is a side elevation of a prior art sports surface based on marketing literature;

[0031]FIG. 3 is a stylized side elevation of a two yarn component embodiment of the present invention;

[0032]FIG. 4 is a stylized side elevation of a three yarn component embodiment of the present invention;

[0033]FIG. 5 is a illustration of length and shape variations in knit-deknit yarns;

[0034]FIG. 6 is a side elevation of a four yarn component embodiment of the present invention employing heavy denier, knit-deknit yarn for the lower pile height tufts.

DETAILED DESCRIPTION OF THE DRAWINGS

[0035]FIGS. 1 and 2 illustrate various prior art sports surfaces using in-fill techniques.

[0036]FIG. 1 is a side elevation of a prior art synthetic grass turf assembly as depicted in FIG. 2 of U.S. Pat. No. 5,958,527. The grass turf assembly 10 includes a flexible open weave backing 12 and upstanding synthetic ribbons 14, which are tufted in spaced-apart rows. An in-fill layer 16 is disposed between the ribbons. The in-fill is made up of sand granules 18 and resilient rubber granules 20, arranged in layers of different sand-rubber proportions.

[0037]FIG. 2 is a side elevation of a prior art turf system (AstroPlay™) as depicted in marketing literature for the product. The turf system product 20 includes a fiber glass backing 32 and polyethylene fibers 34. A 100% particulate rubber in-fill 36 is used. Texturized nylon fibers 38 are said to stabilize the fill.

[0038] In contrast to the above, in the present invention a dense layer of yarn tufts, rather than a particular in-fill, maintains the tall, grass-blade-like yarn segments in a generally vertical orientation through a significant portion of the length of such segments. In preferred embodiments, the dense layer of yarn tufts is formed from yarn made in accordance with the teachings of application Ser. No. 09/392,260 to Auguste et al., filed Sep. 9, 1999 entitled “KNIT-DEKNIT YARN AND METHOD AND APPARATUS FOR MAKING SAME”, the contents of which are hereby incorporated by reference in their entirety.

[0039] The sports surface of the present invention can be made on conventional carpet tufting machinery. The general tuft arrangement will now be discussed with reference to the side elevations of FIGS. 3 and 4 which have been simplified to illustrate the tufting procedure. The sports surface 100 includes a suitable flexible backing such as the open weave flexible backing 102 of a weight sufficient to withstand forces encountered when the surface is in use and to maintain the sports surface in contact with, for example, an adhesive coated playing field substrate surface. A first yarn 104 is tufted at spaced intervals in the backing and provides generally upwardly extending segments suggestive of blades of grass. A second yarn 106 (and in the case of the product of FIG. 4, a third yarn 108) provides yarn segments in supporting layer 110 below the tops of the first yarn segments. In preferred embodiments, the second yarn segments 106 (and third yarn segments 108) are made of a heavy denier knit-deknit yarn and have a length under tension approximately equal to the length L of the first yarn segments. The second (and third) yarn segments form a layer having a vertical height less than L. The second (and third) yarn segments are sufficiently numerous and of sufficient bulk to maintain the first yarn segments in an approximately vertical orientation in the layer without requiring the addition of particulate fill. (Note that the necessary density is more accurately depicted in FIG. 6). Upper portions of the first yarn segments may lay over as shown in the Figures.

[0040] The machines in general use for tufting carpet are capable of tufting carpet at one pile height. They are adjustable to a specific pile height, but once set, all thread lines are cut at the same pile height (cut pile carpet). The present invention overcomes this tufting machine limitation by threading the tufting machine with conventional straight yarn in thread line A (FIGS. 3 and 4), and with knit-deknit textured yarn in thread line B (and C in the case of FIG. 4). The tufting machine then tufts all thread lines to the same height by holding all the yarns under tension as the stitch is made and then cutting the yarn to form the cut pile tuft. Once the sports surface is coated with either a latex or polyurethane coating and the carpet is heated to cure the backing material, the knit-deknit yarn tufts will pull down into their preset textured patterns. The making, properties and use of such knit-deknit yarns are described in detail in the above-mentioned U.S. patent application Ser. No. 09/392,260.

[0041] Conventional tufting machines are characterized by a machine gauge, i.e. a fixed distance between adjacent needles or tufts in a row. Table I lists some typical gauges. For standard carpet, there are preferred ranges of yarn denier which can be tufted at each gauge. These ranges are also listed in Table I. TABLE I Tufting Machine Gauge (distance between needles and/or tufts in a row in inches) Fraction ⅛ {fraction (3/16)} ¼ {fraction (5/16)} ⅜ {fraction (7/16)} ½ {fraction (9/16)} ⅝ {fraction (11/16)} ¾ Decimal 0.1250 0.1875 0.2500 0.3125 0.3750 0.4375 0.5000 0.56 0.63 0.69 0.75 Denier Low 1000 1850 1850 3000 4500 5700 7600 7600 7600 7600 7600 Range High 5700 8000 8000 10000 10000 10000 10000 10000 10000 15000 15000

[0042] It will be understood that various combinations of yarn tufts and tuft spacings can be obtained by feeding the appropriate yarn types to selected ones of the tufting needles of a conventional tufting machine. For example, two types of yarn A and B can be interspersed on a ¼″ gauge machine by feeding grass blade or straight shag yarn to every other needle and feeding knit-deknit yarn to the remaining needles. As shown in FIG. 3, the spacing between adjacent A and B tufts is G (¼ inch in this example) and the spacing between adjacent A tufts is twice G (½ inch in this example). Where three yarn types A, B and C are used, the resulting product may be as depicted in FIG. 4. Again, assuming that the gauge is ¼ inch, the spacing between adjacent A shag or blade tufts is now three times G (¾ inch in this example).

[0043] In a similar fashion, for example, the spacing and amount of stabilizing second yarn tufts B can be doubled relative to the shag or blade yarn tufts A by appropriate selection of yarn feeds to the tufting machine needles. To continue with this example, in a ⅛″ gauge machine, A tufts can be placed at ¾− intervals. Two B tufts could be evenly spaced between the A tufts, i.e. at ¼″ and ½″ needle locations. The other needles need not be used, or could be used to tuft a third yarn type C in the spaces between the A and B yarn segments.

[0044] As shown in Table I, a range of yarn deniers may be used, the range depending on tuft separation. The ranges in denier are from 1,000 to 15,000 and above. The face fiber in the thread rows can vary to include polyethylene, Nylon and polypropylene. The Nylon and polypropylene yarns, if used, may need to be modified to lower the coefficient of friction, thus making the yarn more slippery than typical unmodified Nylon or polypropylene fibers. Various advantages and properties can be achieved by combining different types of fibers. For example:

[0045] 1. Nylon fiber is inherently the most resilient of these fibers it resists compacting under heavy use better than the other fibers. Nylon has the best general reputation for overall quality among these fibers. A disadvantage is that it has the highest cost of these three fibers.

[0046] 2. Polypropylene fiber is the lowest cost of these fibers and has a long tradition of successful use in sports surfaces. Its disadvantages are similar to Nylon in that it is more abrasive (less slippery) than polyethylene fiber.

[0047] 3. Polyethylene fiber is the least abrasive (most slippery) of these fibers and intermediate in cost. Its durability in sports surfaces is still somewhat in question as it has been in use less than one half as long as Nylon or polypropylene in sports surfaces and even less than that in open construction with sand and rubber in-filling.

[0048] As noted above, the typical machine available for sports carpet tufting is capable of cutting only one pile height. In accordance with a preferred embodiment of the present invention, different apparent pile heights are achieved using the currently available tufting machines by cutting all thread lines at the same pile height in the tufting machine. The yarn is kept under tension in a stretched out configuration while the cutting is done. When the cutting is complete the tension is relieved. The straight non-textured yarn will remain at its full vertical height while the knit-deknit, heat textured yarn will relax and tend to return to its textured configuration and a lower vertical height. This effect is illustrated by example in FIG. 5. The yarn length of the stitch determines the full vertical height of the non-textured yarn. The final vertical height of the textured yarn will be determined by the degree of kinking of the yarn and subsequent heat treatment. In knit-deknit yarn the yarn has a configuration generally sinusoidal in shape. This shape is approximately characterizable by an amplitude A (wave height) and a wavelength λ as explained in the above-mentioned Auguste et al. patent application. In FIG. 5 segment lengths of 4λ of each of three types of yarn are shown. As noted in the Figure the pile or vertical height of each segment is different for each yarn type. By appropriate selection of λ and A, various vertical heights can be achieved with yarn segments having the same overall length to create a supporting layer for the taller blade or shag segments.

[0049] Table II provides some examples of finished pile height for a three yarn type sports surface such as that shown in FIG. 4: TABLE II Number of Wavelengths Final Pile Height (λs) per Segment A Tuft Long(L) = X N/A B Tuft Medium(M) = 50 to 90% of X 2 to 5 C Tuft Short(S) = 10 to 50% of X 4 to 8

[0050] In preferred embodiments of the present invention, the height X is greater than 1 inch and preferably less than about 3 inches. In more preferred embodiments the height X is from 1.5 inch to 2.5 inch. The selection of X is dictated to some extent on the use environment for which the sport surface is designed. Thus, for example, if the surface is to be used for equestrian activities a height X of greater than 3 inches might be preferable, whereas the preferable height X for a miniature golf putting green would be considerably less.

[0051] An illustration of preferred polymer types and pile heights are set out in Table III below. In this Table it is assumed that reduction in frictional force is desirable in the sport(s) for which the surface is used and/or is desirable to increase the durability of the sports surface. TABLE III Yarn Modified PILE HEIGHT Type Unmodified A B C D PE Unmodified L M or S M or S M or S PE Modified L M or S M or S M or S NYLON Unmodified M or S M or S M or S NYLON Modified L M or S M or S M or S PP Unmodified M or S M or S M or S PP Modified L M or S M or S M or S

[0052]FIG. 6 is an example of a preferred embodiment of the sports surface of the present invention. It assumes a machine gauge, G, of ¼ inch. The yarn is a fibrillated twisted polyethylene yarn of 8000 D. The pile height of L_(A) of the A yarn is 2 inches. Tufts of yarn A are separated in the row by a distance of 4×G (1″ in the example). The A yarn segments 200 may be twisted or flat. The A segments are supported in a generally vertical orientation and cushioning is provided by three other yarn types B, C and D. The B yarn 202 is an 8000 D knit-deknit polyethylene yarn with a final pile height of 1.5 inches. The B yarn provides apparent bulk to the A yarn segments and reduces friction as the A and B yarns move relative to one another. The C and D yarns are each 8000 D knit-deknit nylon yarns for improved wear. The amplitude and λ values of these yarns are selected so that the C and D yarn segments (204 and 206 respectively) have lower pile heights (L_(C) and L_(D)) than the B yarn segments in the finished sports surface.

[0053] As shown in FIG. 6, the supporting layer is a dense intertwined mat of yarn segments B, C and D. In the example given about 75 % of the face weight of the yarn in the sports surface is contained in the yarns B, C and D and only about 25 % is contained in the upstanding segments made of yarn A. In preferred embodiments an equal or greater yarn weight is contained in the supporting layer than in the shag or blade yarn segments (A).

[0054] While the invention has been described with reference to certain examples and preferred embodiments, these should be regarded as illustrative rather than restrictive. The subject matter regarded by the inventor as his invention is set forth in the following claims. 

I claim:
 1. A synthetic sports surface comprising: a flexible backing; a first yarn tufted at spaced intervals in said backing to provide first yarn segments extending upwardly from said backing suggestive of blades of grass; and a second yarn tufted in the intervals between said first yarn, to provide second yarn segments; wherein the second yarn segments are a texturized yarn having a length under tension approximately equal to that of the first yarn segments; wherein the second yarn segments form a layer having a lower vertical height than the first yarn segments; and wherein the second yarn segments are sufficiently numerous and of sufficient dimension to maintain the first yarn segments in an approximately vertical orientation in use without requiring the provision of a particulate fill.
 2. The synthetic sports surface of claim 1, wherein the second yarn is a knit-deknit yarn having a kinked form.
 3. The synthetic sports surface of claim 2, wherein the second yarn has a denier of at least
 7000. 4. The synthetic sports surface of claim 1, further comprising a third yarn tufted in the intervals between the first yarn to provide third yarn segments, which together with the second yarn segments form the mat which maintains the first yarn segments in an approximately vertical orientation.
 5. The synthetic sports surface of claim 2, wherein the first, second and third yarns are of different denier.
 6. The synthetic sports surface of claim 1, wherein the first yarn is a twisted fibrillated, polyethylene tape yarn.
 7. The synthetic sports surface of claim 1, wherein the first yarn segments extend upwardly from the backing from 2 to 3 inches.
 8. The synthetic sports surface of claim 1, wherein the first yarn is made from a thermoplastic having a coefficient of friction lower than unmodified nylon.
 9. The synthetic sports surface of claim 8, wherein the first yarn is made from a nylon modified with an additive for lowering the coefficient of friction selected from the group comprising silicone and Teflon.
 10. A game playing surface having first upstanding tufts of polymeric yarn at least one inch in height, tufted at intervals of at least ½ inch and having second, tufts of knit-deknit yarn located around the upstanding tufts wherein the upstanding tufts extend upwardly beyond the second tufts and wherein at least about half of the yarn face weight is contained in the second tufts.
 11. A method of making a sports surface comprising: providing a carpet tufting machine for producing rows of tufts in a backing with a separation distance G; feeding a first yarn to the tufting machine for producing first tufts at line separations no less than twice G to form tufts of vertical length L; feeding a second, knit-deknit yarn to the tufting machine for producing second tufts between said first tufts, said second tufts having a length under tension approximately equal to the height L; and heat treating the tufted backing to cause the yarn of the second tufts to tend to return to their knitted shape, thereby forming a supporting base for maintaining the first tufts in an approximately vertical orientation.
 12. The method of claim 11, wherein at least about half of the yarn face weight is contained in the second tufts.
 13. The method of claim 12, wherein the denier of the yarn of the second tufts is at least about
 7000. 14. The method of claim 11, wherein the separation between first tufts in a row is at least about ½ inch. 